Variation among Lap Length and Development Length (Anchorage)
The reinforcement bars are mainly arranged to transmit the load from member to member i.e. either to another rebar or to concrete.
To transmit the load from one member to another securely & efficiently, reinforcement bars should have been tightly attached at both ends to resist skidding of the bars.
Lap Length: Lap length stands for the length of the overlap of bar necessary for securely delivering stress from one bar to another. Lap length varies in case of tension and compression zones and primarily based on concrete and steel. When, it is required to lap bars with various dia, the length is dependent on smaller dia.
The rebars are available in specific length. If the rebar has to be expanded apart from that limit, then there should be adequate lap length to safely transfer the load.
Lap length varies on the basis of tension (at bottom of a beam) and compression zones (at top of beam) and various factors like grade of concrete, rebar size, concrete cover etc affect the lap length.
Development Length: Development length stands for the length of the bar essential to transmit stress from steel to concrete.
As per IS456, the computed tension or compression in any bar at any section should be developed on each side of the section with an accurate development or by end anchorage or with a combination thereof.
As per IS 456:2000, the computed tension or compression in any bar at any section should be formed on every side of the section with proper development length or with an end anchorage to resist skidding of the member from the support.
Such length should be arranged in a continuous beam, cantilever slabs and other critical joints (beam-column). It will be supplied as a bend where the restraining member is thin similar to an end beam as demonstrated under (Ld).
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